Convection

Convection is the main mode of heat transfer in liquids and gases.
It is the process by which heat is transmitted from one place to another by the movement of heated particles of gas or liquid.

Convection only takes place in gases and liquids, but not in solids as the particles cannot move far away from their places in solids. It is the particles in hot liquid or gas that transmit the heat energy. It involves the movement of the hotter fluids form the hot region to the cool region.

How Convection Work
When liquid is being heated, the layer of water that is closer to the heat source will expand and become less dense as compared to the layer of water above. Expanded water will then rise while the layer of water that is not expanded will sink. This is then called the convection current.